The Anglo-Irish Treaty was signed between representatives of the British government and envoys plenipotentiary (ie, negotiators empowered to sign a treaty without reference back to their superiors) of the Irish Republic in December 1921.

Among its main clauses were that:

British Crown forces would withdraw from Ireland for the first time in eight hundred years;

The new Irish state, called the Irish Free State or Saorstát Éireann (pronounced sare-staut air-inn), was to have the King as part of its internal system of governance and to represented by a Representative of the Crown;

Members of the new Free State's parliament would be required to take an Oath of Allegiance 'to the Free State'. A secondary part of the Oath was to be of fidelity to 'King George V. his heirs and successors' as part of the Treaty settlement;

Opponents of the Treaty mounted a military campaign of opposition which produced the Irish Civil War (1922-23). In 1922, its two main Irish signatories, President Griffith and Michael Collins both died. Griffith died partially from exhaustion. Collins, at the signing of the Treaty, said that in signing it, he may have signed his 'actual death warrant'. He was correct. he was assassinated by anti-Treaty republicans in Beal na mBlath[?] in August 1922, barely a week after Griffith's death. Both men were replaced in their posts by W.T. Cosgrave.

The Treaty's provisions relating to the Crown, governor-generalship and its superiority in law were all repealed from the 1922 Constitution by Eamon de Valera, who became President of the Executive Council of the Irish Free State (prime minister) in 1932. Collins argued that the Treaty would give 'the freedom to achieve freedom'. De Valera himself acknowledged the accuracy of this claim both in his actions in the 1930s but also in words he used to describe his opponents and what they did during the 1930s. 'They were magnificent', he told his son in 1932, just after he had entered government and read the files left by Cosgrave's Cumann na nGaedhael Executive Council.

Most people in Ireland today, including members of de Valera's own party, Fianna Fáil agree that it was a mistake to oppose the Treaty and that it was the best deal on offer for the Irish. Britain in 1922 was never going to grant Ireland an independent republic, not least because it could not afford to, without facing similar demands from its dominions. What Ireland got, dominion status on a par of that enjoyed by Canada, New Zealand and Australia, was a massive advance on the forms of Home Rule offered and accepted by Irish leaders like John Dillon[?], John Redmond and Charles Stewart Parnell.

Furthermore (though it was not generally realised at the time), the IRA was weeks from collapse, with little ammunition or weaponry left. When Collins first heard that the British had called a Truce in mid 1921, following King George V's appeal for reconciliation at the opening of the Northern Ireland, parliament, he commented "we thought they were mad." For the British, though they never realised it, were weeks, perhaps even days away from defeating an exhausted IRA.

De Valera was once asked in a private conversation what had been his biggest mistake. His answer was blunt: "not accepting the Treaty." Current Taoiseach (prime minister and leader of Fianna Fáil) Bertie Ahern has conceded that the date that marks the real achievement of independence is 1922, when the Irish Free State created by the Anglo-Irish Treaty came into being.